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<H2><A NAME="SECTION03222000000000000000">
Data Types and Precision</A>
</H2>

<P>
LAPACK provides the same range of functionality for <B>real</B>
and <B>complex</B> data.

<P>
For most computations there are matching
routines, one for real and one for complex data,
but there are a few exceptions. For example, corresponding to the routines
for real symmetric indefinite systems of linear equations, there are
routines for complex Hermitian and complex symmetric systems,
because both types of complex systems occur in practical applications.
However, there is no complex analogue of the routine for finding
selected eigenvalues of a real symmetric tridiagonal matrix,
because a complex Hermitian matrix can always be reduced to
a real symmetric tridiagonal matrix.
<A NAME="1184"></A>

<P>
Matching routines for real and complex data have been coded
to maintain a close correspondence between the two, wherever possible.
However, in some areas (especially the nonsymmetric eigenproblem) the
correspondence is necessarily weaker.

<P>
All routines in LAPACK are provided in both <B>single</B> and
<B>double</B> precision versions. The double precision versions have
been generated automatically, using Toolpack/1&nbsp;[<A
 HREF="node151.html#Toolpack">88</A>].

<P>
Double precision routines for complex matrices require the
non-standard Fortran data type COMPLEX*16, which is available on
most machines where double precision computation is usual.

<P>
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<ADDRESS>
<I>Susan Blackford</I>
<BR><I>1999-10-01</I>
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